Design Techniques for High Efficiency Highly Linear RF Power Amplifer

Abstract

Power consumption is a key parameter to be considered in designing wireless systems, especially for cellular applications. Lower power consumption by designing highly power efficient transceiver circuits is extremely desirable as it results in lower battery size, higher talk time, lower heat generation and lower cost. Very high spectral efficiency is sought after in present day communication systems. In order to achieve very high data rates, sophisticated non-constant envelope modulation schemes are used. This places very stringent requirements on the transceiver design. One of the key requirements is spectral linearity or purity, wherein the transmitter signal spectrum has to be clean within the signal bandwidth and outside the signal bandwidth as specified by FCC regulations for the wireless standard.

Output RF power amplifier (PA) consumes most of the power in a transmitter and is the key to high efficiency transmitter design. This research focuses on novel techniques to maximize power efficiency of the RF power amplifier and at the same time having high spectral linearity to meet FCC specifications. This research attempts to achieve the goal of high efficiency and high linearity by two different methods - signal conditioning and smart circuit design.

A new crest factor reduction (CFR) technique to developed to reduce peak to average ratio (PAR) of high PAR signals. Trade-offs between the in-band and out-of-band distortion is analyzed for maximum reduction in PAR of the signal. A novel high efficiency linear transmitter architecture based on power quadrature modulation is proposed. High efficiency differential class D power supply modulator is designed in Jazz 0.18 um process.

A lookup table based digital predistortion (DPD) engine is developed in MATLAB to improve linearity performance in RF power amplifier. A DPD algorithm is demonstrated to improve the distortion performance of a Gallium Nitride RF PA at a particular output power level.